The present invention relates to microelectronic packaging. Microelectronic chips typically are thin, flat bodies with oppositely facing, generally planar front and rear surfaces and with edges extending between these surfaces. Chips generally have contacts on the front surface, which are electrically connected to the circuits within the chip. Certain chips require a protective element, referred to herein as a cap, lid or cover, over all or part of the front surface. For example, chips having optoelectronic devices, e.g., image sensors or light emitting devices and the like incorporate optically active regions on their front surfaces, which are best protected from physical and chemical damage by a cap, lid or cover.
Certain other types of devices such as microelectromechanical or “MEMS” chips include microscopic electromechanical devices, e.g., acoustic transducers such as microphones, which must be covered by a cap. The caps used for MEMS and SAW chips must be spaced from the front surface of the chip to an open gas-filled or vacuum void beneath the cap in the active area, so that the cap does not touch the acoustical or mechanical elements. Voltage controlled oscillators (VCOs) sometimes also require a cap to be placed over the active area.
Desirably, protective lids or caps are added to such units by processing which is efficient and which provides reliable protection for the sensitive devices early in the packaging process.